A second copy kept somewhere the first disaster cannot reach. A backup on the same machine is not a backup — it burns with everything else.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a spare key at your sister's house.
For example
The laptop is dropped in the kitchen and never wakes up again. Every photograph is still safe, because a copy sits on a little drive in a drawer upstairs.
This is one card out of 275.
The hundred words you meet most are free — the whole set, animated, in one file that works with no internet.
Volume 1 has all 275 in fifteen chapters, with Staying Safe the largest chapter on purpose.